This consists of:
* String#html_safe! a method to mark a string as 'safe'
* ActionView::SafeBuffer a string subclass which escapes anything unsafe which is concatenated to it
* Calls to String#html_safe! throughout the rails helpers
* a 'raw' helper which lets you concatenate trusted HTML from non-safety-aware sources (e.g. presantized strings in the DB)
* New ERB implementation based on erubis which uses a SafeBuffer instead of a String
Hat tip to Django for the inspiration.